Exhaust gas emitted from an internal combustion engine is a heterogeneous mixture that contains gaseous emissions such as, but not limited to, carbon monoxide (“CO”), unburned hydrocarbons (“HC”) and oxides of nitrogen (“NOx”), as well as condensed phase materials (liquids and solids) that constitute particulate matter (“PM”). Catalyst compositions, typically disposed on catalyst supports or substrates, are provided in an engine exhaust system as part of an aftertreatment system to convert certain, or all of these exhaust constituents into non-regulated exhaust gas components.
One type of exhaust treatment technology for reducing emissions is a particulate filter (“PF”). The PF is designed to remove diesel particulate matter, or soot, from exhaust gas of an engine. The particulate matter removed from the exhaust gas is entrapped by, and entrained in, the PF. When accumulated soot reaches a predetermined level the PF is either replaced or regenerated. Replacement or regeneration facilitates that soot removal continues at desired parameters. In addition, many engines include an oxidation catalyst (“OC”) that oxidizes hydrocarbons and carbon monoxide into carbon dioxide and water to further reduce emissions.
In certain arrangements, a motor vehicle may also include a hydrocarbon injector (HCI) that introduces hydrocarbons into exhaust gases to increase exhaust gas temperature. The increase in exhaust gas temperature heats the OC to improve catalytic performance. The introduction of hydrocarbons and added heat also reduces contaminant build up in the OC and PF. Failure of the HCI is often misdiagnosed as a failure of the OC. Replacing the OC unnecessarily is a costly and time consuming process that may lead to customer dissatisfaction. Accordingly, it is desirable to provide a testing system that can more accurately detect a faulty HCI. In addition, it is desirable to provide a testing system that can differentiate between a faulty HCI and a faulty OC.